Summary Report No. 44

Capabilities and Limitations of Physically Based Hydrological Modelling on the Hillslope ScaleA. Bronstert (April 1998)

Hillslope
hydrological modelling is considered to be of great importance for the
understanding and quantification of hydrological processes in hilly or
mountainous landscapes. In recent years a few comprehensive
hydrological models have been developed at the hillslope scale which
have resulted in an advanced representation of hillslope hydrological
processes (including their interactions), and in some operational
applications, such as in runoff and erosion studies at field scale or
lateral flow simulation in environmental and geo-technical engineering.

In this paper an overview on the objectives for hillslope
hydrological modelling is given, followed by a brief introduction of an
exemplary comprehensive hillslope model, which simulates a series of
hydrological processes such as interception, evapotranspiration,
infiltration into the soil matrix and into macropores, lateral and
vertical subsurface soil water flow both in the matrix and preferential
flow paths, surface runoff and channel discharge. Several examples of
this model are presented and discussed in order to figure out the
model's capabilities and limitations. Finally, conclusions about the
limitations of detailed hillslope modelling are drawn and an outlook on
the future prospects of hydrological models on the hillslope scale is
given.

The presented model performed reasonable calculations of Hortonian
surface runoff and subsequent erosion processes, given detailed
information of initial soil water content and on soil hydraulic
conditions. The vertical and lateral soil moisture dynamics were also
represented quite well. However, the given examples of model
applications show that quite detailed climatic and soil data is
required to obtain satisfactory results. The limitations of detailed
hillslope hydrological modelling arise from different points:
difficulties in the representations of certain processes (e.g. surface
crusting, unsaturated-saturated soil moisture flow, macropore flow),
problems of small scale variability, a general scarcity of detailed
soil data, uncomplete process parametrization, and problems with the
interdependent linkage of several hillslopes and channel-hillslope
interactions.